The present invention relates generally to the clamping of elastomeric hose and tubing to fixtures and hose coupling devices, such as stems and coupling inserts, and to the use of bands formed from an at-least-twice-oriented polymer having a shrinkage response to each of at least two diameter reducing release temperatures, to provide improved constrictive forces about elastomeric hose and tubing. More particularly, this invention relates to an improved elastomeric hose and tubing clamp formed from a band of an at-least-twice-oriented polymer, which is simpler to install than prior art clamps. Specifically, this invention relates to an improved clamp for sealing hose and tubing to coupling devices associated with automotive coolant systems.
Reinforced elastomeric hose and tubing, hereinafter generically referred to as hose, are commonly used to convey various fluids which may be under a variety of pressures and temperatures as part of fluid transport systems. For these systems to operate effectively, the connections between the hose and the stems, couplings or other fixtures must be fluid tight and must be able to resist separations caused by fluid pressure. This mode of separation is known as blow-off. Separation of the hose from the fixtures may also occur as a result of environmental interference, which mode of separation is known as pull-off.
Connections between hose and couplings or other fixtures are commonly made by placing the open end of a hose over e.g., a stem. The hose and the associated fixture are ordinarily sized and shaped to allow the open end of the hose to slip over the fixture, and to securely seat about same. In moderate temperature or pressure environments such a fit is generally sufficient. More typically however, a hose clamp is applied about the hose near the open end thereof for urging the hose more tightly about the stem or insert in order to resist leakage, blow-off and pull-off.
Hose clamps have been produced in various sizes and shapes, and have been made of various materials. A number of prior art hose clamp designs, along with summaries of their respective deficiencies, are described in U.S. Pat. No. 5,340,167. Common deficiencies of prior art hose clamps include the corrosion of metal clamps, the danger of hose damage due to sharp metal edges, clamp protrusions necessitating specific axial and circumferential placement of the clamp and occupying valuable space in the hose environment, and the difficulty in utilizing rapid automated assembly line-type installation techniques with these clamps. Additionally, most prior art hose clamps have insufficient self-adjustment characteristics, that is, an inability to expand and contract to follow the expansion and contraction of the clamped materials.
The most prevalent and persistent problem affecting prior art hose clamps in modern automotive coolant systems is an inability to resist cold leaks over time. Cold leakage generally occurs when the coolant system is cold. While such leaks in older systems are more common, new systems are not immune to the problem. Cold leakage results from the combined effects of the compression set of the hose material and the contraction of the hose as temperatures drop. The compressive force exerted by the hose clamp combined with the exposure to high temperature over time provided by the flow of coolant as it cycles through the system cause the hose material to flow away from the clamped site. This phenomenon is a consequence of the compression set of the hose material. As the coolant system further cycles and coolant flows away from the clamped area, exposing this area to relatively cold temperatures, the now thinner hose segment in the area of the clamp slips away from the clamp, effectively breaking the seal and resulting in a cold leak.
Cold leakage is exacerbated when the hose clamp employed exerts a non-uniform constrictive force about the circumference of the hose, whereby separation between the stem and the hose occurs, again breaking the seal and resulting in leakage. Such non-uniformity can furthermore lead to leakage at times other than when the system is cold. Generally, the discontinuities found in many prior art hose clamps rendered such clamps highly susceptible to cold leakage.
For purposes of the present disclosure, the term "dynamic hoop stress" will be used to signify the constrictive force per unit area a hose clamp exerts upon the clamped object as a result of the inner diameter of the clamp being actively reduced. The term, "static hoop stress" will be used to signify the constrictive force per unit area the clamp exerts upon the clamped object in countering an expansive force exerted by the clamped object. This is typically attributable to the fluid pressure present during fluid transfer, and also includes the effect of the thermal expansion of the elastomeric hose about which the band is clamped. The dynamic and static hoop stresses required of a particular clamp depend upon the application requirements.
An improvement in hose clamp design over traditional forms is the subject of the aforementioned U.S. Pat. No. 5,340,167, and involves a heat shrinkable polymer band having a single diameter reducing release temperature, which may be placed over an elastomeric hose and stem or other coupling device. The application of this clamp generally involves placing the clamp loosely about the hose at its connection end, placing the connection end about the stem or insert, and then heating the clamp to a predesignated temperature at which point shrinkage occurs. The point at which shrinkage occurs is referred to as the diameter reducing release temperature. The temperature is maintained at or about the release temperature at least until the clamp shrinks down to fit securely about the connection end. As the material of the polymeric clamp is fairly flexible and the shape of the clamp is without significant discontinuities, it can be seen that the constrictive force applied by the clamp is substantially uniform.
The heat shrinkable polymer hose clamp offers significantly improved self-adjustment characteristics and excellent dynamic and static hoop stresses for improved resistance to blow-off and pull-off compared to other more traditional styles of hose clamp, and it is furthermore devoid of projections which otherwise waste space, require specific axial or rotational positioning, and are a source of injury or the collection of debris. This type of clamp also conforms well to irregularities in stem and insert shapes. Installation of the clamp however, requires the relatively cumbersome and awkward use of a heat source at the installation site to induce engagement of the clamp with the hose connection end. This is especially difficult in assembly-line type environments where different types of hose connection systems may be installed on automotive equipment. For example, hose connection systems may be configured in a variety of directions, e.g., horizontally and vertically; they may come in an array of diameters; they may be located in relatively confined, tight areas surrounded by other equipment. In addition, heat must be applied for a period of time sufficient for proper engagement of the clamp and the hose; this may require from several seconds to several minutes depending on the clamp size and location, which operation is time-consuming and generally impractical in assembly line settings. One also may be required locate additional power sources along the assembly lines to accommodate the use of heat sources.
Satisfactory application of the heat shrinkable band is moreover highly sensitive to operator error; if heat is not applied uniformly, the band may not fit correctly, resulting in increased potential for leakage. To ensure uniform heat distribution, the use of a device or heat monitor may be required. Likewise, if the clamp is not applied in the correct position, perfect heat distribution may not compensate for misfit which also increases the possibility of leakage. A hose clamp that is self-adjusting, is capable of exhibiting a uniform constrictive force about the connection end of hose, is capable of improved dynamic and static hoop stresses, and which may be applied to hose connection ends easily and without the external application of heat has not heretofore been known.